Monday 2 January 2012 03.20 EST
First published on Monday 2 January 2012 03.20 EST

"Everyone is entitled to their opinion" – a refrain commonly heard in our society. We value free speech and the rights of the individual. The private preferences we keep, as long as they do not interfere with the rights and freedoms of others, are ours to do with as we wish.

What uproar there would be if a government minister announced that, in future, only scarves of a certain colour would be acceptable on days of national celebration. The calls for resignation would be immediate and severe: "Who do they think they are, trying to tell us what we can and can't do?"; "What is this, a police state?"; "Freedom to do as he pleases is an Englishman's right. It's what our forefathers fought for." Quite right too; democracy is best served by the maintenance of civil liberties and the sharpening of one's mind against the potential for tyranny.

Children learn this central tenet early on and soon become adept at deploying it to suit their own purposes. The phrase "well it's just my opinion" can act as a get-out clause which avoids further questioning or the need to give an explanation. A student, when faced with the prospect of concerted thinking, may well prefer to put up a brick wall and so dodge the difficult task of providing a justification for their perspective. They know the sacred position freedom of speech holds for all of us; they know how to confound a questioner by calling this keystone to their defence; and they know the taboo around challenging the opinions of others when they do not impact adversely on anyone else.

This can make things hard for the teacher. We want to promote tolerance and respect in our classrooms and give young people a sense this is how one ought to behave. Yet, we are also seeking to develop rationality, reason and critical thinking. To some extent, there is an air of moral relativism swirling about. That is, the idea that people's views carry equal weight because all individuals ought to be treated equally.

Treating people equally is distinct from treating what they say with equal weight, though. It is self-evident that an argument predicated on logic, experience or evidence outstrips one blandly asserted or supported by nothing other than the individual's will. We need to make clear to students that the right to one's opinions does not negate the need to support them with argument when called to do so.

Justification is the signal difference between opinion and argument. Opinions are stated; arguments are advanced. Opinions are given; arguments are proposed. When we ask a student to explain themselves, we are asking them to give us something which will lend credibility to what they have said. We are asking them to convince us, to persuade us, to show us the legitimacy of what it is they are saying.

It is simply not good enough, in the context of education, to assert one's right to an opinion. Students must be made aware of this. They must be shown clearly the different rules which apply to private and public worlds. The classroom is a public space. It is provided for students in the knowledge that it is our duty to educate them as best we can; to pass on the knowledge and skills that our society has, and continues, to accumulate. As this duty is incumbent upon us, so the duty to participate is incumbent upon them – not that they will necessarily like it!

I have found one of the best ways to discourage bland assertion is to consistently model reasoning with your classes. This can be done in many ways: explaining why it is you have praised a certain pupil's work; rationalising the choice of activities you have opted for; showing the logical steps you went through when creating a series of questions. And, of course, justifying your own opinions. Acting in such a way gives one the moral authority to bat the "well it's just my opinion phrase" back at the student and demand an answer that is not only better, but justifiably better as well.

• Mike Gershon is a social science teacher currently working in central London. He was educated at York University and the University of London in History, Sociology and Citizenship Education. He has been interested in teaching and learning since beginning his PGCE and enjoys creating resources which benefit teachers and students alike.

Do you have something you want to share with colleagues – a resource of your own and why it works well with your students, or perhaps a brilliant piece of good practice in teaching or whole school activity that you know about it? If so please get in touch. If you would like to blog on the Guardian Teacher Network please email emma.drury@guardian.co.uk and please don't be shy about commenting on blogs on this page.